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<a class="jxr_linenumber" name="1" href="#1">1</a>   <em class="jxr_comment">/*</em>
<a class="jxr_linenumber" name="2" href="#2">2</a>   <em class="jxr_comment"> * Licensed to the Apache Software Foundation (ASF) under one or more</em>
<a class="jxr_linenumber" name="3" href="#3">3</a>   <em class="jxr_comment"> * contributor license agreements.  See the NOTICE file distributed with</em>
<a class="jxr_linenumber" name="4" href="#4">4</a>   <em class="jxr_comment"> * this work for additional information regarding copyright ownership.</em>
<a class="jxr_linenumber" name="5" href="#5">5</a>   <em class="jxr_comment"> * The ASF licenses this file to You under the Apache License, Version 2.0</em>
<a class="jxr_linenumber" name="6" href="#6">6</a>   <em class="jxr_comment"> * (the "License"); you may not use this file except in compliance with</em>
<a class="jxr_linenumber" name="7" href="#7">7</a>   <em class="jxr_comment"> * the License.  You may obtain a copy of the License at</em>
<a class="jxr_linenumber" name="8" href="#8">8</a>   <em class="jxr_comment"> *</em>
<a class="jxr_linenumber" name="9" href="#9">9</a>   <em class="jxr_comment"> *     <a href="http://www.apache.org/licenses/LICENSE-2.0" target="alexandria_uri">http://www.apache.org/licenses/LICENSE-2.0</a></em>
<a class="jxr_linenumber" name="10" href="#10">10</a>  <em class="jxr_comment"> *</em>
<a class="jxr_linenumber" name="11" href="#11">11</a>  <em class="jxr_comment"> * Unless required by applicable law or agreed to in writing, software</em>
<a class="jxr_linenumber" name="12" href="#12">12</a>  <em class="jxr_comment"> * distributed under the License is distributed on an "AS IS" BASIS,</em>
<a class="jxr_linenumber" name="13" href="#13">13</a>  <em class="jxr_comment"> * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.</em>
<a class="jxr_linenumber" name="14" href="#14">14</a>  <em class="jxr_comment"> * See the License for the specific language governing permissions and</em>
<a class="jxr_linenumber" name="15" href="#15">15</a>  <em class="jxr_comment"> * limitations under the License.</em>
<a class="jxr_linenumber" name="16" href="#16">16</a>  <em class="jxr_comment"> */</em>
<a class="jxr_linenumber" name="17" href="#17">17</a>  <strong class="jxr_keyword">package</strong> org.apache.commons.configuration.interpol;
<a class="jxr_linenumber" name="18" href="#18">18</a>  
<a class="jxr_linenumber" name="19" href="#19">19</a>  <strong class="jxr_keyword">import</strong> java.lang.reflect.Field;
<a class="jxr_linenumber" name="20" href="#20">20</a>  <strong class="jxr_keyword">import</strong> java.util.HashMap;
<a class="jxr_linenumber" name="21" href="#21">21</a>  <strong class="jxr_keyword">import</strong> java.util.Map;
<a class="jxr_linenumber" name="22" href="#22">22</a>  
<a class="jxr_linenumber" name="23" href="#23">23</a>  <strong class="jxr_keyword">import</strong> org.apache.commons.lang.ClassUtils;
<a class="jxr_linenumber" name="24" href="#24">24</a>  <strong class="jxr_keyword">import</strong> org.apache.commons.lang.text.StrLookup;
<a class="jxr_linenumber" name="25" href="#25">25</a>  <strong class="jxr_keyword">import</strong> org.apache.commons.logging.Log;
<a class="jxr_linenumber" name="26" href="#26">26</a>  <strong class="jxr_keyword">import</strong> org.apache.commons.logging.LogFactory;
<a class="jxr_linenumber" name="27" href="#27">27</a>  
<a class="jxr_linenumber" name="28" href="#28">28</a>  <em class="jxr_javadoccomment">/**</em>
<a class="jxr_linenumber" name="29" href="#29">29</a>  <em class="jxr_javadoccomment"> * &lt;p&gt;</em>
<a class="jxr_linenumber" name="30" href="#30">30</a>  <em class="jxr_javadoccomment"> * A specialized lookup implementation that allows access to constant fields of</em>
<a class="jxr_linenumber" name="31" href="#31">31</a>  <em class="jxr_javadoccomment"> * classes.</em>
<a class="jxr_linenumber" name="32" href="#32">32</a>  <em class="jxr_javadoccomment"> * &lt;/p&gt;</em>
<a class="jxr_linenumber" name="33" href="#33">33</a>  <em class="jxr_javadoccomment"> * &lt;p&gt;</em>
<a class="jxr_linenumber" name="34" href="#34">34</a>  <em class="jxr_javadoccomment"> * Sometimes it is necessary in a configuration file to refer to a constant</em>
<a class="jxr_linenumber" name="35" href="#35">35</a>  <em class="jxr_javadoccomment"> * defined in a class. This can be done with this lookup implementation.</em>
<a class="jxr_linenumber" name="36" href="#36">36</a>  <em class="jxr_javadoccomment"> * Variable names passed in must be of the form</em>
<a class="jxr_linenumber" name="37" href="#37">37</a>  <em class="jxr_javadoccomment"> * {@code mypackage.MyClass.FIELD}. The {@code lookup()} method</em>
<a class="jxr_linenumber" name="38" href="#38">38</a>  <em class="jxr_javadoccomment"> * will split the passed in string at the last dot, separating the fully</em>
<a class="jxr_linenumber" name="39" href="#39">39</a>  <em class="jxr_javadoccomment"> * qualified class name and the name of the constant (i.e. &lt;strong&gt;static final&lt;/strong&gt;)</em>
<a class="jxr_linenumber" name="40" href="#40">40</a>  <em class="jxr_javadoccomment"> * member field. Then the class is loaded and the field's value is obtained</em>
<a class="jxr_linenumber" name="41" href="#41">41</a>  <em class="jxr_javadoccomment"> * using reflection.</em>
<a class="jxr_linenumber" name="42" href="#42">42</a>  <em class="jxr_javadoccomment"> * &lt;/p&gt;</em>
<a class="jxr_linenumber" name="43" href="#43">43</a>  <em class="jxr_javadoccomment"> * &lt;p&gt;</em>
<a class="jxr_linenumber" name="44" href="#44">44</a>  <em class="jxr_javadoccomment"> * Once retrieved values are cached for fast access. This class is thread-safe.</em>
<a class="jxr_linenumber" name="45" href="#45">45</a>  <em class="jxr_javadoccomment"> * It can be used as a standard (i.e. global) lookup object and serve multiple</em>
<a class="jxr_linenumber" name="46" href="#46">46</a>  <em class="jxr_javadoccomment"> * clients concurrently.</em>
<a class="jxr_linenumber" name="47" href="#47">47</a>  <em class="jxr_javadoccomment"> * &lt;/p&gt;</em>
<a class="jxr_linenumber" name="48" href="#48">48</a>  <em class="jxr_javadoccomment"> *</em>
<a class="jxr_linenumber" name="49" href="#49">49</a>  <em class="jxr_javadoccomment"> * @version $Id: ConstantLookup.java 1210218 2011-12-04 20:57:48Z oheger $</em>
<a class="jxr_linenumber" name="50" href="#50">50</a>  <em class="jxr_javadoccomment"> * @since 1.4</em>
<a class="jxr_linenumber" name="51" href="#51">51</a>  <em class="jxr_javadoccomment"> * @author &lt;a</em>
<a class="jxr_linenumber" name="52" href="#52">52</a>  <em class="jxr_javadoccomment"> * href="<a href="http://commons.apache.org/configuration/team-list.html" target="alexandria_uri">http://commons.apache.org/configuration/team-list.html</a>"&gt;Commons</em>
<a class="jxr_linenumber" name="53" href="#53">53</a>  <em class="jxr_javadoccomment"> * Configuration team&lt;/a&gt;</em>
<a class="jxr_linenumber" name="54" href="#54">54</a>  <em class="jxr_javadoccomment"> */</em>
<a class="jxr_linenumber" name="55" href="#55">55</a>  <strong class="jxr_keyword">public</strong> <strong class="jxr_keyword">class</strong> <a href="../../../../../org/apache/commons/configuration/interpol/ConstantLookup.html">ConstantLookup</a> <strong class="jxr_keyword">extends</strong> StrLookup
<a class="jxr_linenumber" name="56" href="#56">56</a>  {
<a class="jxr_linenumber" name="57" href="#57">57</a>      <em class="jxr_javadoccomment">/**</em><em class="jxr_javadoccomment"> Constant for the field separator. */</em>
<a class="jxr_linenumber" name="58" href="#58">58</a>      <strong class="jxr_keyword">private</strong> <strong class="jxr_keyword">static</strong> <strong class="jxr_keyword">final</strong> <strong class="jxr_keyword">char</strong> FIELD_SEPRATOR = '.';
<a class="jxr_linenumber" name="59" href="#59">59</a>  
<a class="jxr_linenumber" name="60" href="#60">60</a>      <em class="jxr_javadoccomment">/**</em><em class="jxr_javadoccomment"> An internally used cache for already retrieved values. */</em>
<a class="jxr_linenumber" name="61" href="#61">61</a>      <strong class="jxr_keyword">private</strong> <strong class="jxr_keyword">static</strong> Map&lt;String, String&gt; constantCache = <strong class="jxr_keyword">new</strong> HashMap&lt;String, String&gt;();
<a class="jxr_linenumber" name="62" href="#62">62</a>  
<a class="jxr_linenumber" name="63" href="#63">63</a>      <em class="jxr_javadoccomment">/**</em><em class="jxr_javadoccomment"> The logger. */</em>
<a class="jxr_linenumber" name="64" href="#64">64</a>      <strong class="jxr_keyword">private</strong> Log log = LogFactory.getLog(getClass());
<a class="jxr_linenumber" name="65" href="#65">65</a>  
<a class="jxr_linenumber" name="66" href="#66">66</a>      <em class="jxr_javadoccomment">/**</em>
<a class="jxr_linenumber" name="67" href="#67">67</a>  <em class="jxr_javadoccomment">     * Tries to resolve the specified variable. The passed in variable name is</em>
<a class="jxr_linenumber" name="68" href="#68">68</a>  <em class="jxr_javadoccomment">     * interpreted as the name of a &lt;b&gt;static final&lt;/b&gt; member field of a</em>
<a class="jxr_linenumber" name="69" href="#69">69</a>  <em class="jxr_javadoccomment">     * class. If the value has already been obtained, it can be retrieved from</em>
<a class="jxr_linenumber" name="70" href="#70">70</a>  <em class="jxr_javadoccomment">     * an internal cache. Otherwise this method will invoke the</em>
<a class="jxr_linenumber" name="71" href="#71">71</a>  <em class="jxr_javadoccomment">     * {@code resolveField()} method and pass in the name of the class</em>
<a class="jxr_linenumber" name="72" href="#72">72</a>  <em class="jxr_javadoccomment">     * and the field.</em>
<a class="jxr_linenumber" name="73" href="#73">73</a>  <em class="jxr_javadoccomment">     *</em>
<a class="jxr_linenumber" name="74" href="#74">74</a>  <em class="jxr_javadoccomment">     * @param var the name of the variable to be resolved</em>
<a class="jxr_linenumber" name="75" href="#75">75</a>  <em class="jxr_javadoccomment">     * @return the value of this variable or &lt;b&gt;null&lt;/b&gt; if it cannot be</em>
<a class="jxr_linenumber" name="76" href="#76">76</a>  <em class="jxr_javadoccomment">     * resolved</em>
<a class="jxr_linenumber" name="77" href="#77">77</a>  <em class="jxr_javadoccomment">     */</em>
<a class="jxr_linenumber" name="78" href="#78">78</a>      @Override
<a class="jxr_linenumber" name="79" href="#79">79</a>      <strong class="jxr_keyword">public</strong> String lookup(String <strong class="jxr_keyword">var</strong>)
<a class="jxr_linenumber" name="80" href="#80">80</a>      {
<a class="jxr_linenumber" name="81" href="#81">81</a>          <strong class="jxr_keyword">if</strong> (<strong class="jxr_keyword">var</strong> == <strong class="jxr_keyword">null</strong>)
<a class="jxr_linenumber" name="82" href="#82">82</a>          {
<a class="jxr_linenumber" name="83" href="#83">83</a>              <strong class="jxr_keyword">return</strong> <strong class="jxr_keyword">null</strong>;
<a class="jxr_linenumber" name="84" href="#84">84</a>          }
<a class="jxr_linenumber" name="85" href="#85">85</a>  
<a class="jxr_linenumber" name="86" href="#86">86</a>          String result;
<a class="jxr_linenumber" name="87" href="#87">87</a>          <strong class="jxr_keyword">synchronized</strong> (constantCache)
<a class="jxr_linenumber" name="88" href="#88">88</a>          {
<a class="jxr_linenumber" name="89" href="#89">89</a>              result = constantCache.get(<strong class="jxr_keyword">var</strong>);
<a class="jxr_linenumber" name="90" href="#90">90</a>          }
<a class="jxr_linenumber" name="91" href="#91">91</a>          <strong class="jxr_keyword">if</strong> (result != <strong class="jxr_keyword">null</strong>)
<a class="jxr_linenumber" name="92" href="#92">92</a>          {
<a class="jxr_linenumber" name="93" href="#93">93</a>              <strong class="jxr_keyword">return</strong> result;
<a class="jxr_linenumber" name="94" href="#94">94</a>          }
<a class="jxr_linenumber" name="95" href="#95">95</a>  
<a class="jxr_linenumber" name="96" href="#96">96</a>          <strong class="jxr_keyword">int</strong> fieldPos = <strong class="jxr_keyword">var</strong>.lastIndexOf(FIELD_SEPRATOR);
<a class="jxr_linenumber" name="97" href="#97">97</a>          <strong class="jxr_keyword">if</strong> (fieldPos &lt; 0)
<a class="jxr_linenumber" name="98" href="#98">98</a>          {
<a class="jxr_linenumber" name="99" href="#99">99</a>              <strong class="jxr_keyword">return</strong> <strong class="jxr_keyword">null</strong>;
<a class="jxr_linenumber" name="100" href="#100">100</a>         }
<a class="jxr_linenumber" name="101" href="#101">101</a>         <strong class="jxr_keyword">try</strong>
<a class="jxr_linenumber" name="102" href="#102">102</a>         {
<a class="jxr_linenumber" name="103" href="#103">103</a>             Object value = resolveField(<strong class="jxr_keyword">var</strong>.substring(0, fieldPos), <strong class="jxr_keyword">var</strong>
<a class="jxr_linenumber" name="104" href="#104">104</a>                     .substring(fieldPos + 1));
<a class="jxr_linenumber" name="105" href="#105">105</a>             <strong class="jxr_keyword">if</strong> (value != <strong class="jxr_keyword">null</strong>)
<a class="jxr_linenumber" name="106" href="#106">106</a>             {
<a class="jxr_linenumber" name="107" href="#107">107</a>                 <strong class="jxr_keyword">synchronized</strong> (constantCache)
<a class="jxr_linenumber" name="108" href="#108">108</a>                 {
<a class="jxr_linenumber" name="109" href="#109">109</a>                     <em class="jxr_comment">// In worst case, the value will be fetched multiple times</em>
<a class="jxr_linenumber" name="110" href="#110">110</a>                     <em class="jxr_comment">// because of this lax synchronisation, but for constant</em>
<a class="jxr_linenumber" name="111" href="#111">111</a>                     <em class="jxr_comment">// values this shouldn't be a problem.</em>
<a class="jxr_linenumber" name="112" href="#112">112</a>                     constantCache.put(<strong class="jxr_keyword">var</strong>, String.valueOf(value));
<a class="jxr_linenumber" name="113" href="#113">113</a>                 }
<a class="jxr_linenumber" name="114" href="#114">114</a>                 result = value.toString();
<a class="jxr_linenumber" name="115" href="#115">115</a>             }
<a class="jxr_linenumber" name="116" href="#116">116</a>         }
<a class="jxr_linenumber" name="117" href="#117">117</a>         <strong class="jxr_keyword">catch</strong> (Exception ex)
<a class="jxr_linenumber" name="118" href="#118">118</a>         {
<a class="jxr_linenumber" name="119" href="#119">119</a>             log.warn(<span class="jxr_string">"Could not obtain value for variable "</span> + <strong class="jxr_keyword">var</strong>, ex);
<a class="jxr_linenumber" name="120" href="#120">120</a>         }
<a class="jxr_linenumber" name="121" href="#121">121</a> 
<a class="jxr_linenumber" name="122" href="#122">122</a>         <strong class="jxr_keyword">return</strong> result;
<a class="jxr_linenumber" name="123" href="#123">123</a>     }
<a class="jxr_linenumber" name="124" href="#124">124</a> 
<a class="jxr_linenumber" name="125" href="#125">125</a>     <em class="jxr_javadoccomment">/**</em>
<a class="jxr_linenumber" name="126" href="#126">126</a> <em class="jxr_javadoccomment">     * Clears the shared cache with the so far resolved constants.</em>
<a class="jxr_linenumber" name="127" href="#127">127</a> <em class="jxr_javadoccomment">     */</em>
<a class="jxr_linenumber" name="128" href="#128">128</a>     <strong class="jxr_keyword">public</strong> <strong class="jxr_keyword">static</strong> <strong class="jxr_keyword">void</strong> clear()
<a class="jxr_linenumber" name="129" href="#129">129</a>     {
<a class="jxr_linenumber" name="130" href="#130">130</a>         <strong class="jxr_keyword">synchronized</strong> (constantCache)
<a class="jxr_linenumber" name="131" href="#131">131</a>         {
<a class="jxr_linenumber" name="132" href="#132">132</a>             constantCache.clear();
<a class="jxr_linenumber" name="133" href="#133">133</a>         }
<a class="jxr_linenumber" name="134" href="#134">134</a>     }
<a class="jxr_linenumber" name="135" href="#135">135</a> 
<a class="jxr_linenumber" name="136" href="#136">136</a>     <em class="jxr_javadoccomment">/**</em>
<a class="jxr_linenumber" name="137" href="#137">137</a> <em class="jxr_javadoccomment">     * Determines the value of the specified constant member field of a class.</em>
<a class="jxr_linenumber" name="138" href="#138">138</a> <em class="jxr_javadoccomment">     * This implementation will call {@code fetchClass()} to obtain the</em>
<a class="jxr_linenumber" name="139" href="#139">139</a> <em class="jxr_javadoccomment">     * {@code java.lang.Class} object for the target class. Then it will</em>
<a class="jxr_linenumber" name="140" href="#140">140</a> <em class="jxr_javadoccomment">     * use reflection to obtain the field's value. For this to work the field</em>
<a class="jxr_linenumber" name="141" href="#141">141</a> <em class="jxr_javadoccomment">     * must be accessable.</em>
<a class="jxr_linenumber" name="142" href="#142">142</a> <em class="jxr_javadoccomment">     *</em>
<a class="jxr_linenumber" name="143" href="#143">143</a> <em class="jxr_javadoccomment">     * @param className the name of the class</em>
<a class="jxr_linenumber" name="144" href="#144">144</a> <em class="jxr_javadoccomment">     * @param fieldName the name of the member field of that class to read</em>
<a class="jxr_linenumber" name="145" href="#145">145</a> <em class="jxr_javadoccomment">     * @return the field's value</em>
<a class="jxr_linenumber" name="146" href="#146">146</a> <em class="jxr_javadoccomment">     * @throws Exception if an error occurs</em>
<a class="jxr_linenumber" name="147" href="#147">147</a> <em class="jxr_javadoccomment">     */</em>
<a class="jxr_linenumber" name="148" href="#148">148</a>     <strong class="jxr_keyword">protected</strong> Object resolveField(String className, String fieldName)
<a class="jxr_linenumber" name="149" href="#149">149</a>             <strong class="jxr_keyword">throws</strong> Exception
<a class="jxr_linenumber" name="150" href="#150">150</a>     {
<a class="jxr_linenumber" name="151" href="#151">151</a>         Class&lt;?&gt; clazz = fetchClass(className);
<a class="jxr_linenumber" name="152" href="#152">152</a>         Field field = clazz.getField(fieldName);
<a class="jxr_linenumber" name="153" href="#153">153</a>         <strong class="jxr_keyword">return</strong> field.get(<strong class="jxr_keyword">null</strong>);
<a class="jxr_linenumber" name="154" href="#154">154</a>     }
<a class="jxr_linenumber" name="155" href="#155">155</a> 
<a class="jxr_linenumber" name="156" href="#156">156</a>     <em class="jxr_javadoccomment">/**</em>
<a class="jxr_linenumber" name="157" href="#157">157</a> <em class="jxr_javadoccomment">     * Loads the class with the specified name. If an application has special</em>
<a class="jxr_linenumber" name="158" href="#158">158</a> <em class="jxr_javadoccomment">     * needs regarding the class loaders to be used, it can hook in here. This</em>
<a class="jxr_linenumber" name="159" href="#159">159</a> <em class="jxr_javadoccomment">     * implementation delegates to the {@code getClass()} method of</em>
<a class="jxr_linenumber" name="160" href="#160">160</a> <em class="jxr_javadoccomment">     * Commons Lang's</em>
<a class="jxr_linenumber" name="161" href="#161">161</a> <em class="jxr_javadoccomment">     * &lt;code&gt;&lt;a href="<a href="http://commons.apache.org/lang/api-release/org/apache/commons/lang/ClassUtils.html" target="alexandria_uri">http://commons.apache.org/lang/api-release/org/apache/commons/lang/ClassUtils.html</a>"&gt;</em>
<a class="jxr_linenumber" name="162" href="#162">162</a> <em class="jxr_javadoccomment">     * ClassUtils&lt;/a&gt;&lt;/code&gt;.</em>
<a class="jxr_linenumber" name="163" href="#163">163</a> <em class="jxr_javadoccomment">     *</em>
<a class="jxr_linenumber" name="164" href="#164">164</a> <em class="jxr_javadoccomment">     * @param className the name of the class to be loaded</em>
<a class="jxr_linenumber" name="165" href="#165">165</a> <em class="jxr_javadoccomment">     * @return the corresponding class object</em>
<a class="jxr_linenumber" name="166" href="#166">166</a> <em class="jxr_javadoccomment">     * @throws ClassNotFoundException if the class cannot be loaded</em>
<a class="jxr_linenumber" name="167" href="#167">167</a> <em class="jxr_javadoccomment">     */</em>
<a class="jxr_linenumber" name="168" href="#168">168</a>     <strong class="jxr_keyword">protected</strong> Class&lt;?&gt; fetchClass(String className) <strong class="jxr_keyword">throws</strong> ClassNotFoundException
<a class="jxr_linenumber" name="169" href="#169">169</a>     {
<a class="jxr_linenumber" name="170" href="#170">170</a>         <strong class="jxr_keyword">return</strong> ClassUtils.getClass(className);
<a class="jxr_linenumber" name="171" href="#171">171</a>     }
<a class="jxr_linenumber" name="172" href="#172">172</a> }
</pre>
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